The present invention is directed to the field of mine roof expansion anchors which are installed together with a two-part resin grouting mix to provide a combined mechanical-chemical anchor for an elongated roof bolt. More specifically, the invention concerns unique structure associated with the mechanical anchor to assist in mixing the initially flowable components of the resin mix, and to methods of installation of mine roof support systems including such anchors.
Mechanical expansion anchors have for many years provided a popular means of anchoring elongated bolts in drill holes in a rock structure. The bolts carry a bearing plate which is urged into contact with the surface of the rock structure as the bolt is tensioned to several thousand pounds, thereby supporting and reinforcing the rock structure adjacent the mine tunnel or passageway.
Chemical anchors, i.e., a plurality of initially flowable materials which harden after combination in the drill hole, have also been widely used to anchor roof bolts in drill holes. In fact, it has become common practice to use both a mechanical and a chemical anchor to firmly secure the distal end of a mine roof bolt in a drill hole. The resin mix components are isolated from one another in a two-compartment, elongated cartridge which is inserted into the drill hole in advance of the distal, threaded end of the bolt which carries the expansion anchor. The cartridge is fractured against the blind end of the drill hole as the bolt is fully inserted, allowing the grouting components to flow around the expansion anchor and the upper end of the bolt.
Earlier forms of chemical anchors required more thorough mixing of the components upon release from the cartridge and longer hardening times than currently available materials. Accordingly, the prior art includes a number of structural elements and installation methods devised to ensure proper mixing of the grouting components. Although the hydraulic action of the components produced by forceful fracture of the cartridge and the few seconds of bolt rotation required to set the mechanical anchor provide essentially all the mixing necessary for modern day grouting materials, it is still desirable to enhance the mixing to some extent, particularly in the area below the anchor, if this can be accomplished economically.
It is a principal object of the present invention to provide a novel and improved mine roof expansion anchor having means for enhancing the mixing of grouting mix components installed concurrently with the expansion anchor without significantly increasing the cost or installation time of the anchor.
Another object is to provide a combination mechanical-chemical anchor for a mine roof bolt wherein the mechanical portion includes novel and improved means for enhancing the mixing of chemical components as the bolt is rotated to set the expansion anchor.
A further object is to provide a novel and improved method of supporting and stabilizing a rock formation by enhancing the mixing of two, initially flowable components of a grouting mix within a drill hole in the course of setting a mechanical expansion anchor.
Still another object is to provide a combined resin-mechanical roof bolt anchor having novel and improved means for mixing the resin grouting components in the area of the drill hole below the expansion shell and plug.
Other objects will in part be obvious and will in part appear hereinafter.